If we will just going to be Biblical then if you were a christian then you will not going to celebrate fiesta because even in the Holy Bible there is no such Christian celebrating fiesta unless to the Gentiles and Hebrews,or even Birthday there is no record in the scriptures says it so that they are celebrating, Be biblical ,so it is also written in the Holy Scripture in 1 Corinthian 4:6 b " .....that you may learn from us believing of the saying that Thou shall not go beyond what was written" so Hope that this helped you even just it is a little thing, thank you and God Bless.
